Evaluation of structural in¯uence on performance of shape memory alloy linear actuators by sharp phase front-based constitutive models A. Bhattacharyya a, * , V. Stoilov a , O. Iliev b a Department of Mechanical Engineering, 4-9 Mechanical Engineering Building, University of Alberta, Edmonton, Alta., Canada T6G 2G8 b Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, Acad. G. Bonchev. Str., Bl.8, BG-11113, So®a, Bulgaria Received 20 December 1999; accepted 22 March 2000 Abstract This paper analyzes and compares the predictions of two sharp phase-front based shape memory alloy (SMA) constitutive models ± proposed by Abeyaratne and Knowles (R. Abeyaratne, J. Knowles, Journal of Mechanics and Physics of Solids 41 (1993) 541) and Bruno et al. (O. Bruno, P. Leo, F. Reitich, Phys. Rev. Lett. 74 (1995) 746±749) ± in the context of an SMA linear actuator (an SMA rod or a wire) actuated electrically and subjected to spring-loaded boundary conditions at its ends. Both models are then used to analyze the performance ± i.e., speci®c energy output and energy eciency ± of the SMA actuator. The computational modeling is done using a moving boundary ®nite element method (MBFEM)-based numerical approach proposed by Stoilov et al. (V. Stoilov, O. Iliev, A. Bhattacharyya, Computer Methods in Applied Mechanics and Engineering, accepted). It is seen that while both models produce somewhat diering predictions of the SMA response, the dierence is not dramatic enough to prefer one model to another. Predictions of the SMA actuator performance indicate that there is an optimum spring stiness at which the energy eciency of the SMA actuator is at its maximum. This raises the possibility that when an SMA actuator is integrated into a structure, the passive components of the structure may play a key role in determining the optimum energy eciency of the active structural component (the SMA actuator) during the activation of the structure. Ó 2000 Elsevier Science B.V. All rights reserved. Keywords: SMA actuator; Performance measures; SMA computational modeling 1. Introduction Two issues that are of central importance in actuator design with shape memory alloys (SMAs) are: 1. Availability of an appropriate constitutive model to characterize the response of shape memory alloys, 2. evaluation of SMA actuator response based on a certain commonly accepted de®nitions of actuator performance. The ®rst issue is complicated by the fact that the phase trans- formations in shape memory alloys are accompa- nied by a strong coupling between the thermal and mechanical ®elds in the SMA actuator. Another important fact is that the phase transformation is largely inhomogeneous in nature, accompanied by www.elsevier.com/locate/commatsci Computational Materials Science 18 (2000) 269±282 * Corresponding author. Tel.: +1-780-492-3705; fax: +1-780- 492-2200. E-mail address: a.bhatta@ualberta.ca (A. Bhattacharyya). 0927-0256/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 5 6 ( 0 0 ) 0 0 1 0 6 - 3